地基GPS遥感的祁连山区夏季可降水量日变化特征及成因分析

Characteristics and Cause of Diurnal Variation of Precipitable Water Vapor Derived from Ground-Based GPS in Qilian Mountains in Summer

基于祁连山区2007年7～8月地基GPS遥感的大气可降水量(Precipitable Water,PW)资料、探空资料和自动气象站资料,采用谐波分析等方法,分析了祁连山区夏季PW的日变化特征,并初步探讨其成因。结果表明:祁连山区夏季PW具有明显的日变化特征。PW日变化特征在无降水日比有降水日更显著。日循环(24 h)与半日循环(12 h)是PW日变化的主要信号。在无降水日,PW日变化以日循环为主,振幅为0.8～1.6 mm,峰值出现的时间在18:00～21:00(北京时,下同)。半日循环的振幅为0.6～0.7 mm,峰值出现的时间在05:00～06:00和17:00～18:00。在有降水日,不同站点PW日变化特征有所不同,有的以日循环为主导,有的以半日循环为主导。PW日变化与逐时累积降水频次日变化具有明显的先后关系,两者日变化的位相差为2.5 h。PW日变化与气温和比湿等要素的日变化以及山谷风演变有关。

Based on the precipitable water（PW） derived from ground-based GPS and the observations from radiosondes and automatic weather stations in Qilian mountains of Northwestern China during the period of July～August 2007,the diurnal variations of PW are systematically investigated.The results show that PW exhibited a pronounced diurnal variation in Qilian Mountains in summer.The diurnal variations of PW without precipitation days are more prominent than with precipitation days.The diurnal（24 h） and semidiurnal（12 h） cycles of the PW are fitted using the harmonic analysis method.The results show that the diurnal and semidiurnal cycles together can represent the diurnal variations very well.During the without precipitation days,diurnal cycle,which explains over 76% of the subdaily variance,has an amplitude of 0.8～1.6 mm and peaks appear at 18：00～21：00.The semidiurnal cycle is generally weaker,with an amplitude of 0.6～0.7 mm,and peaks appear in 05：00～06：00 and 17：00～18：00 respectively.However,during the with precipitation days,the characteristics of diurnal variation of PW at different stations are different.At some stations,the diurnal cycle explains more the subdaily variance than semidiurnal cycle.At other stations the semidiurnal cycle is more significant than diurnal cycle.The causes of diurnal variation of PW are preliminarily discussed.It can be seen that the diurnal variations of PW occur prior to the changes of hourly accumulated precipitation frequency.The former phase is two and half hours earlier than that of the latter.The diurnal variations of PW can be affected by surface air temperature,specific humidity and mountain-valley breeze.